I've been using BSE since they started, and the corners are the hardest to do. I also do window tinting so I understand how it works with the solution, if you make the solution too soapy it wont stick, and if you get dust or debris on the skin it wont stick either. Best bet is to use very very little soap in the solution and add a few drops of rubbing alcohol and use a hair dryer for the corners. The hair dryer will evaporate the solution and make the adhesive stick better. I am afraid if its been awhile since you tried to install the skin and it still will not stick, email BSE and tell them the corners wont stick and they will probably send you another skin to try.

It took me a little while to get my iPad mini rear skin secure and the older iPhones with the curved back were also challenging but defiantly doable.